The proposed project has as its major goal the development of methods for identifying prospective victims of sudden death. The importance of premature ventricular contractions (PVCs) will be studied in patients with known coronary artery disease. In addition, studies will be carried out to determine whether beta-blockade therapy will bring about a reduction in both PVCs and sudden death. Other studies will be addressed to interactive effects of antiarrhythmic agents, and in addition the importance of sleep and mild psychic stress on the development of electrical instability. To accomplish the above, a computer system for rapid, accurate analysis of 24-hour 2-channel Holter tapes will be developed. Emphasis will be placed on reasonable cost and ease of replication of the analysis system.